At an ever increasing rate, high speed and high performance transistors are more densely integrated in semiconductor dies. The amount of heat generated by the semiconductor dies increases significantly due to the growth in number of transistors per semiconductor die, the large amount of power passing through the transistors, and the high operation speed of the transistors. If the heat generated by the semiconductor dies cannot be dissipated efficiently, the semiconductor dies may fail to operate or have a degraded operating performance. Accordingly, heat dissipation is an issue in densely integrated semiconductor dies, and efficient heat dissipation is highly desirable.
Semiconductor dies normally reside in or on a substrate and the substrate will affect the semiconductor dies performance in many ways. For instance, the heat produced by the semiconductor dies could be conducted away from their immediate vicinity through the substrate. Laminate materials are widely used in substrates, which are inexpensive and have a mature supply-base within the industry. However, the laminate materials have poor thermal properties. A heat spreader integrated in the substrate is now widely used to enhance the thermal conductivity of the substrate.
FIG. 1 shows a system 10 including a conventional substrate 12. The substrate 12 includes a substrate core 14, connecting structures 16, and a heat spreader structure 18. The substrate core 14 has a top surface and a bottom surface opposite the top surface of the substrate core 14. Each connecting structure 16 extends through the substrate core 14 from the top surface of the substrate core 14 to the bottom surface of the substrate core 14. The heat spreader structure 18 includes a top heat plate 20 residing over a portion of the top surface of the substrate core 14, a bottom heat plate 22 residing over a portion of the bottom surface of the substrate core 14, and a heat spreader 24 extending through the substrate core 14. The heat spreader 24 is in contact with both the top heat plate 20 and the bottom heat plate 22, and coupled to the substrate core 14 via an adhesive 26.
The system 10 also includes a wire-bonding die 28, a printed circuit board (PCB) 30, and a system heat sink 32. The wire-bonding die 28, which includes a wire-bonding die body 34 and wires 36, is attached to the substrate 12. The wire-bonding die body 34 has a top surface and a bottom surface that is opposite the top surface of the wire-bonding die body 34 and coupled to the heat spreader structure 18. Each wire 36 extends from the top surface of the wire-bonding die body 34 towards a corresponding connecting structure 16.
In addition, the PCB 30 is mounted over a portion of the system heat sink 32. In order to connect the connecting structure 16 with the PCB 30 and connect the bottom heat plate 22 with the system heat sink 32 simultaneously, the system heat sink 32 must have a pedestal 38, which extends through the PCB 30, such that a top surface of the pedestal 38 is coplanar with a top surface of the PCB 30. The top surface of the pedestal 38 is in contact with the bottom heat plate 22 and the top surface of the PCB 30 is in contact with the connecting structure 16.
However, forming the pedestal 38 as described above is not cost efficient. Instead, the system heat sink 32 must be machined from an excessively thick starting system heat sink precursor (not shown) in order to form the pedestal 38, which is directly connected to the bottom heat plate 22. The process to form the pedestal 38 is generally expensive and wasteful as well as increases dimensional uncertainty of the layout.
Accordingly, to accommodate the increased heat generation of densely integrated semiconductor dies and reduce the cost of the system heat sink assembly, there remains a need for improved substrate designs. The substrate design will be easily fabricated without increasing the product size.